Question explored with the scientific record
Why do modern humans have such bad teeth?
The short version: the evidence for why modern teeth are worse is thin, but what exists points to fluoride and microbiome shifts as suspects, not diet alone.
The ancient DNA study of Streptococcus mutans found the cariogenic pathogen and its virulence genes present in hunter-gatherers 8,000 years ago [4]. That means the main bug for cavities existed long before agriculture and refined sugar. So diet change is not the whole story. The modern oral microbiome is heavily shaped by fluoride exposure, which the evidence shows is not harmless. A 2025 meta-analysis of 59 studies found a pooled IQ drop of 0.45 standard deviations in children with higher fluoride exposure, p<0.001 [5]. A separate study linked water fluoride to a 64% increase in primary hypothyroidism in pregnant women (OR 1.64) [7]. The salivary proteomics of dental fluorosis revealed immune activation and CFTR disruption, a direct mechanism for enamel damage [6]. These are hard clinical endpoints, not surrogates.
The hunter-gatherer oral microbiome studied from dental calculus showed top genera (Actinomyces, Streptococcus, Propionibacterium) that are still common in modern mouths [2]. That suggests the core players haven't changed, but the balance has. The modern high-sugar diet and fluoride both alter the ecology. The evidence for the net benefit of fluoridation is absent from this retrieval; the harms are documented. The burden of proof is on the intervention.
| Exposure | Outcome | Effect size (95% CI) | Source |
|---|---|---|---|
| Fluoride (children) | IQ reduction | Pooled SMD −0.45 (−0.57 to −0.33) | [5] |
| Water fluoride (pregnant) | Primary hypothyroidism | OR 1.64 (1.04–2.58) | [7] |
| Water fluoride (pregnant) | Hypothyroidism in TPO-negative women | OR 2.80 (1.24–6.36) | [7] |
My call: the hypothesis that modern diet, microbiome changes, and fluoride exposure drive dental decay is plausible, but the evidence is not strong enough to prove it. The known harms of fluoride alone make fluoridation a net risk until proven otherwise.
Sources examined 12
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The human gastroinstestinal tract microbiota in health – current knowledge summary
This literature review summarizes current knowledge on the healthy human gastrointestinal tract microbiota, detailing its composition across oral, esophageal, gastric, and intestinal compartments, the concept of a core microbiome and dysbiosis, and the sequencing-based methods u…
DOI: 10.12775/jehs.2022.12.10.005 -
Genomic ancestry, diet and microbiomes of Upper Palaeolithic hunter-gatherers from San Teodoro cave
An integrative multi-omics study combining ancient human genome sequencing, dental calculus metagenomics, and palaeoproteomics to reconstruct the genomic ancestry, diet, and oral microbiomes of two Upper Palaeolithic hunter-gatherers from San Teodoro cave (Sicily), revealing an …
DOI: 10.1038/s42003-022-04190-2 -
Integrated fecal microbiota and metabolomics analysis of the orlistat intervention effect on polycystic ovary syndrome rats induced by letrozole combined with a high-fat diet
A multi-omics study in a letrozole/high-fat diet–induced rat model of PCOS showing that orlistat attenuates weight gain and improves hormonal and lipid abnormalities, with associated shifts in gut microbiota (e.g., reduced Ruminococcaceae/Lactobacillaceae and increased Muribacul…
DOI: 10.1186/s13048-023-01193-3 -
Exploring the Evolution of the Cariogenic Oral Pathobiont Streptococcus mutans Using Ancient DNA
Using a novel ancient DNA hybridization-capture approach, the study generated genome-wide Streptococcus mutans data from 75 ancient individuals spanning about 8,000 years to characterize virulence gene content and pan-genome evolution, revealing pre-agricultural presence and lim…
DOI: 10.64898/2025.12.02.691581 -
Fluoride Exposure and Children’s IQ Scores
This systematic review and meta-analysis investigates the association between fluoride exposure and children's IQ scores, revealing statistically significant inverse relationships across multiple studies.
DOI: 10.1001/jamapediatrics.2024.5542 -
Salivary Proteomic Signatures Reveal Novel Mechanistic Insights into Moderate Dental Fluorosis Pathogenesis and Oral Homeostasis Disruption
Distinct salivary proteomic changes in moderate dental fluorosis reveal immune activation and metabolic remodeling, with CFTR acting as a central network hub linking fluoride exposure to enamel hypomineralization and disruption of oral homeostasis.
DOI: 10.34133/csbj.0003 -
3 Fluoride Exposure and Hypothyroidism in Pregnant Women: A Potential Mechanism of Fluoride Neurotoxicity
Fluoride exposure during pregnancy is associated with maternal thyroid disruption and potential child IQ effects in Canadian cohorts, with US urinary fluoride patterns showing race/education disparities and metal co-exposures; mediation by maternal thyroid dysfunction is not cle…
DOI: 10.1017/s135561772301069x -
Combined effects of chronic high glucose and fluoride exposure on kidney cells: exploratory in vitro and in vivo study
Chronic hyperglycemia and fluoride exposure were studied for their combined effects on renal cells and kidneys, revealing fluoride's dual role in attenuating diabetes-related glomerular fibrosis while promoting tubular injury at higher doses, with KIM-1 upregulation in vitro and…
DOI: 10.1007/s10735-025-10670-6 -
Genetic and environmental determinants of dental fluorosis: a case‒control study of DLX3, ESR1, and ESR2 variants in a high-fluoride region of Mexico
This cross-sectional case-control study of 79 pregnant women in Durango, Mexico investigated how environmental fluoride exposure and DLX3, ESR1, and ESR2 genetic variants influence dental fluorosis severity, finding protective associations for DLX3 rs2278163 and ESR1 rs12154178 …
DOI: 10.1186/s12903-025-07109-5 -
International fluoride symposium: effects of fluoride on human health and its mechanisms of action – a meeting report
A comprehensive, international symposium-report summarizing fluoride exposure sources, biomarkers, dietary assessment methods, analytical challenges, health outcomes (notably neurodevelopment) and a coordinated research agenda to harmonize birth-cohort studies and advance fluori…
DOI: 10.1186/s12919-025-00345-1 -
Addressing Critiques of the Evidence Linking Fluoride and Children’s IQ
A high-level viewpoint defending a robust inverse association between fluoride exposure and children's IQ while addressing common critiques and emphasizing consistency across study designs and exposure metrics.
DOI: 10.5334/aogh.4853 -
Is Fluoride Blameless?—The Influence of Fluorine Compounds on the Invasiveness of the Human Glioma-like Cell Line U-87
This study investigates the effects of sodium fluoride on the invasiveness of the U-87 human glioblastoma cell line, revealing that fluoride exposure at physiologically relevant concentrations may promote a pro-invasive phenotype through the activation of key signaling pathways.
DOI: 10.3390/ijms252312773